Worst case, a bloating battery cracking open a plastic enclosure or being able to vent gas through the gaps in one would be preferable too, right?

Absolutely and it is why I hate these little pouch cells in wearables. Phones, headphones, in-ear pods, sports gear, toys (which kids take to bed), they're absolutely everywhere and if you look at the way they are usually mounted it is a small miracle there aren't more issues. Powerbanks in particular are a pretty serious hazard.